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XMOS/PCM5102a DAC vs Modded CD63 - New DAC loses - Why?
XMOS/PCM5102a DAC vs Modded CD63 - New DAC loses - Why?
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Old 14th January 2014, 11:00 PM   #1
dwjames is offline dwjames  United Kingdom
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Question XMOS/PCM5102a DAC vs Modded CD63 - New DAC loses - Why?

Hi guys, wondering if you can shed some light / educate me please.

I have a Marantz CD63 which I have modded extensively to include new TX, lots of individual power regulation and decoupling cap upgrades, a high quality TCXO/Flea clock, discrete output stage to sum the DAC outputs and a valve buffer output stage. I have completed most modifications myself, but aside from a bit of re-capping/repairing of old amps, this is my first real DIY Hifi job. I've learned a lot and I'm VERY pleased with the results indeed, the level of clarity, depth and ambience is amazing, way beyond anything I've heard before. It's totally opened my eyes to the world of hifi and I'm re-loving all my music
Here's a picture, so you can see where it's up to (please excuse the mess
Click the image to open in full size.


So when it came to finding a solution for good quality music on a budget for another room, it occurred to me that a large deal of the work on the CD player was to deal with the physical spinning and reading of the disk and if I use FLAC files and go direct to a DAC, all this is bypassed, so it becomes simpler to get good results, so this is what I chose.
My solution is a Wandboard running Community Squeeze as the player, then an XMOS based usb to I2S board and a PCM5102a board both from DIYINHK and both fed by an individually regulated low noise 5v supply. This is the first DAC that I've owned. I didn't choose it for any particular reason other than it seemed to be the latest technology at a reasonable price.
Here's some pics of that:
Click the image to open in full size.
I've added extra tant decoupling caps to the various DAC V+ as there were pads specifically to allow that.
Click the image to open in full size.

(here with a Raspberry Pi rather than the Wandboard)
Click the image to open in full size.

It's a cheap solution, but generally the results are rather good.
I've also done it in a modular fashion so that I can swap and change each bit if necessary.

But... I've A/B compared the 2 players and consistently prefer the CD63. It seems to have a level of detail and clarity which the XMOS/PCM5102a dac just doesn't. I particularly notice the difference in acoustic recordings and specifically stuff like cymbals which seem to have more delicate air and decay with the CD63.

My question is, what am I missing and what can I improve with the DAC? I understand it's a low cost solution, but what's the weak link? If I had to guess, I'd say probably the clock for the DAC? Or should I just use a different USB DAC board that's proven to sound great (any suggestions?)

I'm only playing FLACs ripped from CD, no high res stuff.

Any recommendations for mods/changes/different bits of kit gratefully received. I'm ok to spend a bit more on the components if the results are good.

thanks in advance,
James
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Old 14th January 2014, 11:19 PM   #2
abraxalito is online now abraxalito  United Kingdom
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Looks like you've had a whole barrel of fun with modding

A couple of things stand out - firstly your new DAC has a toroid for the supply, whereas the CD player has an EI trafo. The second of these will have a lower interwinding capacitance and hence introduce less mains-borne noise into your system.

Secondly - don't use tants for your 5V rail decoupling, rather use a lot of ceramics in parallel. I suggest 22uF X7R (or X5R) 1206 size ones. Put them as close to the DAC chip's analog supply pins as you possibly can. This normally means soldering them on top of the chip.

Lastly the PCM5102 has the option of more than one digital filter - the minimum phase filter is reported to sound better. I don't know though how this is selected, presumably over a serial control bus from the XMOS?
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Old 15th January 2014, 02:46 AM   #3
Spartacus is offline Spartacus  United Kingdom
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You maybe be able to squeeze a little more performance from the DAC with various tweaks, but the DAC chip itself is a budget offering, with performance a fair bit behind the state of the art contenders.

Maybe try the AK4399 offering from DIYINHK. The AKM chips reportedly do well in direct out mode - without an output stage - so you wouldn't need an extra +/-15V power supply. There's a build thread on this forum for this DAC.
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Old 17th January 2014, 08:53 AM   #4
dwjames is offline dwjames  United Kingdom
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Quote:
Originally Posted by abraxalito View Post
Looks like you've had a whole barrel of fun with modding

A couple of things stand out - firstly your new DAC has a toroid for the supply, whereas the CD player has an EI trafo. The second of these will have a lower interwinding capacitance and hence introduce less mains-borne noise into your system.
That's just a bad angle on the CD63, I actually have 2 extra Toroidal TX in there, 1 for the servos and feeding the seperate regs, 1 for the valve stage. The standard trafo is just doing the display on the front these days
Click the image to open in full size.


Quote:
Originally Posted by abraxalito View Post
Secondly - don't use tants for your 5V rail decoupling, rather use a lot of ceramics in parallel. I suggest 22uF X7R (or X5R) 1206 size ones. Put them as close to the DAC chip's analog supply pins as you possibly can. This normally means soldering them on top of the chip.
Good call thanks. I'll work out how the pins lie and what the spacing is and get some SMD caps for some ultra-close decoupling.


Quote:
Originally Posted by abraxalito View Post
Lastly the PCM5102 has the option of more than one digital filter - the minimum phase filter is reported to sound better. I don't know though how this is selected, presumably over a serial control bus from the XMOS?
I think on this board, there's the option to change the filters with jumpers/bridges.

Quote:
Originally Posted by Spartacus View Post
You maybe be able to squeeze a little more performance from the DAC with various tweaks, but the DAC chip itself is a budget offering, with performance a fair bit behind the state of the art contenders.

Maybe try the AK4399 offering from DIYINHK. The AKM chips reportedly do well in direct out mode - without an output stage - so you wouldn't need an extra +/-15V power supply. There's a build thread on this forum for this DAC.
Thanks. I've started looking around to see what people are favouring. I don't want to change to something else that I'll be bored of of find the limits of quickly. I think a DDDAC 1794 NOS kit is probably top of my list right now


Lastly.. It's occured to me that if this dac and usb interface is capable of much higher resolution than my 44khz FLAC files are containing, I could use software upsampling with Foobar at a native multiplier of my files to send a higher res signal to the DAC. I appreciate there won't be any additional detail, but if there's 4 times more points to the signal, the DAC should have a better chance of getting it right (or at least that's how it works in my head)
I'll have a play with that.

cheers,
James
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Old 18th January 2014, 07:03 AM   #5
mkusan is offline mkusan  Croatia
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Hello James,
We are in the same boat. My setup Marantz CD-67 (not as tweaked as yours) vs XMOS+AK4396, separate supplies for both. I tried EI transformer, battery, even SMPS, that did not change the result, I still prefer Marantz.

I am afraid upsampling wont bring you audio nirvana

I have yet to try transformer output, but I am not holding my breath, I guess there ain't no such thing as a free lunch.

Please keep us informed upon your progress.

Regards
Marko
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